Over the last few decades, significant advances have been made in electrochemical storage and conversion devices, expanding the capabilities of these systems in a variety of fields including portable electronic devices, air and space craft technologies, and biomedical devices. Current state of the art electrochemical storage and conversion devices tend to have designs and performance attributes specifically selected for compatibility with the diverse range of user applications. For example, current electrochemical storage systems span a range from light weight, stable batteries providing reliable, long runtimes to high capacity batteries capable of providing extremely high discharge rates. Despite recent advances, widespread development and demand for high power portable electronic products has created significant pressure for researchers to develop even more high performance batteries suitable for the wide range of these applications. Furthermore, demands of miniaturization in the field of consumer electronics and instrumentation continue to stimulate research into novel design and material strategies for reducing the sizes, weights and form factors of high performance batteries.
Many recent advances in electrochemical storage and conversion technology are directly attributable to discovery and integration of new materials for battery components. Lithium-ion battery technology, for example, continues to rapidly develop, at least in part, due to the integration of novel cathode and anode materials for these systems. From the pioneering discovery and optimization of intercalated carbon anode materials to more recent discoveries of nanostructured transition metal oxide intercalation cathode materials and nano-phosphate cathode materials, development of new materials has revolutionized the design and performance capabilities of primary and secondary lithium ion batteries. For example, advanced electrode materials have significantly enhanced the energy capacities, energy densities, discharge current rates and cycle life provided by these systems, thus positioning lithium ion batteries to be the preferred technology for the next generation of high-power portable electronic systems, hybrid electric car (HEV) and electric vehicles (EV). Advances in electrode materials also has great promise to positively impact other systems including electrochemical capacitors and supercapacitors, and fuel cells, and is likely to be critical to implementation of these technologies for a range of device applications. Accordingly, the identification and performance evaluation of novel electrode materials is currently a research priority in the development of new and improved electrochemical energy storage and conversion systems.
Electrochemical energy storage and conversion devices use two electrodes; an anode and a cathode, which are electrical conductors, separated by a purely ionic conductor, the electrolyte. The electric current generated during discharge results from chemical reactions and physical processes (e.g., transport) taking place at the electrodes' surfaces, in which positively or negatively charged ions are exchanged with the electrolyte. These processes, in turn, generate or absorb electrons so as to keep the electrical neutrality of the system. The charge exchange induces important modifications in the electrodes surface and bulk structures properties. In particular, charge transfer processes affect each electrode's potential and reaction rate, which set the energy and the power density outputs of an electrochemical power generating device. In the case of a rechargeable battery, for example, the mechanism(s) and extent of changes in the electrodes surface and bulk structure determine the cycle life under specific thermodynamic and kinetic operating conditions (e.g., temperature, charge and discharge voltage limits, current rates and so on).
Knowing the thermodynamics of electrode reactions and physical transformations is essential in predicting the performance and stability of any electrochemical storage and conversion system. For example, important thermodynamic state functions establish, at least in part, the energy, the power and the cycle life of an autonomous electrochemical power source. In fact, the energy density reflects the total amounts of charges reversibly exchanged and the potential at which the exchange occurs. On the other hand, cycle life relates to the stability of states or phases resulting from electrode transformations in the process of charge and discharge. All these processes are controlled, at least to a certain degree, by the thermodynamics of the electrode reactions.
A number of techniques have been developed and applied to evaluating the thermochemical kinetics of electrode reactions including electroanalytical methods (e.g., cyclic voltammetry, potentiometry etc.) and spectroscopic techniques (e.g. x-ray diffraction, NMR, LEEDs, etc.). Given the importance of thermodynamics in virtually all electrochemical energy storage and conversion systems, however, there is currently a need in the art for systems and methods for measuring key thermodynamic parameters, such as changes in entropy, enthalpy and Gibbs free energy, with the accuracy needed for predicting and optimizing the performance attributes and capabilities of these systems. Such systems would play a significant role in identifying new materials for the next generation of electrochemical energy storage and conversion systems, and would significantly contribute to enhancing understanding of the thermochemical kinetics of established cathode and anode materials. New thermodynamic analysis systems also have great potential as versatile test instruments for characterizing materials properties and performance in commercially manufactured electrode systems, including batteries and fuel cells.